Sympathetic discharge and vascular resistance after bed rest.
The effect of -6 degrees head-down-tilt bed rest (HDBR) for 14 days on supine sympathetic discharge and cardiovascular hemodynamics at rest was assessed. Mean arterial pressure, heart rate (n = 25), muscle sympathetic nerve activity (MSNA; n = 16) burst frequency, and forearm blood flow (n = 14) were measured, and forearm vascular resistance (FVR) was calculated. Stroke distance, our index of stroke volume, was derived from measurements of aortic mean blood velocity (Doppler) and R-R interval (n = 7). With these data, an index of total peripheral resistance was determined. Heart rate at rest was greater in the post (71 +/- 2 beats/min)- compared with the pre-HDBR test (66 +/- 2 beats/min; P < 0.003), but mean arterial pressure was unchanged. Aortic stroke distance during post-HDBR (15.5 +/- 1.1 cm/beat) was reduced from pre-HDBR levels (20.0 +/- 1.5 cm/beat) (P < 0.03). Also, MSNA burst frequency was reduced in the post (16.7 +/- 2.8 beats/min)- compared with the pre (25.2 +/- 2.6 beats/min)-HDBR condition (P < 0.01). Bed rest did not alter forearm blood flow, FVR, or total peripheral resistance. Thus reductions in MSNA with HDBR were not associated with a decrease in FVR.
Shoemaker
J K
JK
Division of Cardiology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Hogeman
C S
CS
Leuenberger
U A
UA
Herr
M D
MD
Gray
K
K
Silber
D H
DH
Sinoway
L I
LI
D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D001510:Bed Rest; D001794:Blood Pressure / Q000502:physiology; D005542:Forearm / Q000098:blood supply / Q000502:physiology; D018475:Head-Down Tilt; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D012039:Regional Blood Flow / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology*; D014655:Vascular Resistance / Q000502:physiology*